Aqueous Synthesis of Au10Pt1 Nanorods Decorated with MnO2 Nanosheets for the Enhanced Electrocatalytic Oxidation of Methanol

Developing novel catalysts with high activity and high stability for the methanol oxidation reaction (MOR) is of great importance for the ever-broader applications of methanol fuel cells. Herein, we present a facile technique for synthesizing Au10Pt1@MnO2 catalysts using a wet chemical method and investigate their catalytic performance for the MOR. Notably, the Au10Pt1@MnO2-M composite demonstrated a significantly high peak mass activity of 15.52 A mg(Pt)−1, which is 35.3, 57.5, and 21.9 times greater than those of the Pt/C (0.44 A mg(Pt)−1), Pd/C (0.27 A mg(Pt)−1), and Au10Pt1 (0.71 A mg(Pt)−1) catalysts, respectively. Comparative analysis with commercial Pt/C and Pd/C catalysts, as well as Au10Pt1 HSNRs, revealed that the Au10Pt1@MnO2-M composite exhibited the lowest initial potential, the highest peak current density, and superior CO anti-poisoning capability. The results demonstrate that the introduction of MnO2 nanosheets, with excellent oxidation capability, not only significantly increases the reactive sites, but also promotes the reaction kinetics of the catalyst. Furthermore, the high surface area of the MnO2 nanosheets facilitates charge transfer and induces modifications in the electronic structure of the composite. This research provides a straightforward and effective strategy for the design of efficient electrocatalytic nanostructures for MOR applications.


Introduction
The exceptional performance exhibited by the precious metal Pt in direct methanol fuel cells has established it as a preferred choice among researchers [1][2][3][4].However, its extensive application is hindered by inherent limitations, including the scarcity of Pt, sluggish reaction kinetics, and its susceptibility to CO poisoning [5][6][7][8].To address these limitations, the integration of Pt-based nanostructures with suitable carriers has emerged as a cost-effective and efficient strategy [9][10][11][12][13][14]. Manganese-based materials, recognized for their oxidation capabilities and economic viability, are often employed as catalytic oxidation agents [15][16][17][18].Furthermore, the amalgamation of two-dimensional materials with precious metals holds significant importance in catalysis [19,20].Notably, MnO 2 nanosheets are frequently paired with select precious metals to fabricate composite catalysts owing to their affordability, extensive specific surface area, and abundant binding sites [21][22][23][24].The strong binding affinity and numerous electron transfer pathways exhibited by MnO 2 nanosheets towards the loaded material enable the maximization of their compositional and electronic structural effects [25][26][27].
In recent years, researchers have noted that the strong interaction between active noble metal elements and MnO 2 nanosheets exerts a significant promotional effect on catalytic performance [28][29][30].Li et al. incorporated Au nanoparticles (NPs), synthesized via a hydrothermal method, into metal organic frameworks (Au@MOFs) and immobilized them onto ultra-thin MnO 2 nanosheets to fabricate MnO 2 UNs/Au@PdˆPt nanocube composite nanostructures, featuring ultra-thin MnO 2 nanosheets with a high surface area [24].These nanosheets serve to enhance the dispersibility of Au@PdˆPt nanocube, elevate atomic utilization efficiency, and provide a greater number of catalytically active sites.Additionally, Zhang et al. developed Pt NPs@MnO 2 by cultivating MnO 2 nanosheets on the surface of Pt nanoparticles that were pre-reduced with citric acid using KMnO 4 and ethane sulfonic acid in aqueous solution medium, with the surface of the Pt nanoparticles being enveloped by citrate ions [31].The utilization of citric acid ions as both a template to facilitate the attachment of MnO 2 nanosheets and a reducing agent to promote their formation underscores the multifunctional role of citric acid in the synthesis process.
The challenges associated with the existing composite structures and synthesis methods of MnO 2 nanosheets and metals include the need for numerous synthesis steps, lengthy processing times, non-mild reaction conditions, and unfriendly reactant environments [32][33][34].Furthermore, the limited research regarding the composites of one-dimensional noble metal nanostructures and two-dimensional MnO 2 nanosheets highlights the importance of developing a simpler and milder pathway for preparing composites of precious metals and two-dimensional MnO 2 nanosheets.By addressing these challenges and emphasizing the optimization of the synthesis process, researchers can pave the way for the development of novel composite nanostructures with improved properties and applicability in various catalytic applications.
Motivated by the above considerations, in this work, we developed a facile wet chemical technique to prepare Au 10 Pt 1 @MnO 2 , based on the structure of the Au 10 Pt 1 heterostructure nanorods (HSNRs) prepared in our work [35].By leveraging the excess reducing agent Na 3 C 6 H 5 O 7 present in the Au 10 Pt 1 HSNRs sol, the addition of KMnO 4 solution triggers a redox reaction at 60 • C in an incubator, leading to the formation of the Au 10 Pt 1 @MnO 2 composite catalyst.When compared with commercial Pt/C catalysts, commercial Pd/C catalysts, and Au 10 Pt 1 HSNRs, the Au 10 Pt 1 @MnO 2 -M sample exhibits the lowest initial potential and the highest peak current density in the catalytic methanol oxidation reaction (MOR).This superior performance can be attributed to the unique electronic structure and oxidation capacity of manganese dioxide present in the composite catalyst, highlighting its potential for catalytic applications.

Characterization of Pt/Au@MnO 2 Nanostructures
The MnO 2 nanosheets were synthesized via a wet chemical method, as illustrated in Figure S1.At 45 • C, a specific amount of KMnO 4 and Na 3 C 6 H 5 O 7 solutions were mixed and reacted for 2 h, resulting in the formation of MnO 2 nanosheets.The UV-VIS absorption spectrum of KMnO 4 , depicted in Figure S2a, exhibits an absorption peak in the range of 500-600 nm, which is characteristic of the KMnO 4 solution.Upon the reduction of KMnO 4 to produce MnO 2 nanosheets, the absorption peak observed in the 500-600 nm range dissipates.Instead, a new prominent absorption peak (Figure S2b) emerges within the 300-400 nm range, indicative of the presence of the MnO 2 nanosheet.The TEM in Figure S2c reveal the lamellar structure of the MnO 2 nanosheets.
A wet chemical approach strategy based on the localized surface plasmon resonance (LSPR) effect was used to synthesize Au 10 Pt 1 HSNRs [35].The synthesis methodology encompasses two distinct stages: light nucleation and dark heat reaction.Upon photoexcitation, the LSPR effect of Au NPs facilitates the initial reduction of Pt nucleation on the Au NPs (Figure 1b).Subsequently, the reduction of the Pt precursor occurs in a dark environment at 45 • C, promoting the gradual connection of Au NPs and ultimately leading to the formation of Au 10 Pt 1 HSNRs, as depicted in Figure 1c.Next, the reduction of KMnO 4 was employed to synthesize the Au 10 Pt 1 @MnO 2 composites, as shown in Figure 1d.The morphological evolution from Au NPs to Au 10 Pt 1 HSNRs and ultimately, to the Au 10 Pt 1 @MnO 2 -M composite material (the amount of KMnO 4 added in the preparation process is designated as Au 10 Pt 1 @MnO 2 -L, Au 10 Pt 1 @MnO 2 -M, and Au 10 Pt 1 @MnO 2 -H, respectively, as described in the Section 3.4), is illustrated in Figure 1b-d, demonstrating the successful combination of Au 10 Pt 1 HSNRs with MnO 2 .Throughout this synthesis process, the UV-VIS absorption spectrum of the sample undergoes changes, as shown in Figure 1a.With the formation of the Au 10 Pt 1 @MnO 2 -M composite material, a strong absorption peak in the range of 600-1300 nm is observed, along with a distinct absorption peak representing MnO 2 between 300-400 nm.This indicates the reduction of KMnO 4 to generate MnO 2 nanosheets.TEM images in Figure 1d reveal that the morphology and structure of MnO 2 are largely consistent with those shown in Figure S2c.Locally magnified HRTEM images (Figure 1e) demonstrate that the Au 10 Pt 1 HSNRs retain their original appearance, with a lattice spacing of 0.221 nm in HRTEM confirming the formation of MnO 2 nanosheets (Figure 1f).Furthermore, at this stage, the two-dimensional structure of the MnO 2 nanosheet is predominantly integrated on the surface of the Au 10 Pt 1 HSNRs, as evidenced by the HRTEM image in Figure 1f.The diffraction ring in the selected electron diffraction pattern in Figure 1g further confirms the presence of Au 10 Pt 1 HSNRs and MnO 2 in the composite material.
Au NPs (Figure 1b).Subsequently, the reduction of the Pt precursor occurs in a dark environment at 45 °C, promoting the gradual connection of Au NPs and ultimately leading to the formation of Au10Pt1 HSNRs, as depicted in Figure 1c.Next, the reduction of KMnO4 was employed to synthesize the Au10Pt1@MnO2 composites, as shown in Figure 1d.The morphological evolution from Au NPs to Au10Pt1 HSNRs and ultimately, to the Au10Pt1@MnO2-M composite material (the amount of KMnO4 added in the preparation process is designated as Au10Pt1@MnO2-L, Au10Pt1@MnO2-M, and Au10Pt1@MnO2-H, respectively, as described in the Section 3.4.), is illustrated in Figure 1b-d, demonstrating the successful combination of Au10Pt1 HSNRs with MnO2.Throughout this synthesis process, the UV-VIS absorption spectrum of the sample undergoes changes, as shown in Figure 1a.With the formation of the Au10Pt1@MnO2-M composite material, a strong absorption peak in the range of 600-1300 nm is observed, along with a distinct absorption peak representing MnO2 between 300-400 nm.This indicates the reduction of KMnO4 to generate MnO2 nanosheets.TEM images in Figure 1d reveal that the morphology and structure of MnO2 are largely consistent with those shown in Figure S2c.Locally magnified HRTEM images (Figure 1e) demonstrate that the Au10Pt1 HSNRs retain their original appearance, with a lattice spacing of 0.221 nm in HRTEM confirming the formation of MnO2 nanosheets (Figure 1f).Furthermore, at this stage, the two-dimensional structure of the MnO2 nanosheet is predominantly integrated on the surface of the Au10Pt1 HSNRs, as evidenced by the HRTEM image in Figure 1f.The diffraction ring in the selected electron diffraction pattern in Figure 1g further confirms the presence of Au10Pt1 HSNRs and MnO2 in the composite material.XPS analysis was conducted on the Au 10 Pt 1 @MnO 2 -M composite material to investigate the chemical valence states of each element, as shown in Figure 2. The XPS spectra revealed characteristic peaks of Au, Pt, and Mn elements in the samples.There are peaks of O 1s, C 1s, and Na Auger in the XPS pattern (Figure 2a), in which Na may be derived from the residual ions after the reaction of sodium citrate and then adsorbed on the MnO 2 nanosheets.Peaks at binding energies of 83.8 eV and 87.45 eV, corresponding to Au 0 4f 7/2 and Au 0 4f 5/2 , respectively [36], indicate the presence of Au in a zero valence state.Similarly, peaks at 72.05 eV and 75.45 eV are attributed to Pt 0 4f 7/2 and Pt 0 4f 5/2 , while peaks at 73.45 eV and 76.8 eV correspond to Pt 2+ 4f 7/2 and Pt 2+ 4f 5/2 , respectively [37].In the previous work [35], the Pt element in the structure of Au 10 Pt 1 HSNRs is mainly in a zero-valence state, while in the Au 10 Pt 1 @MnO 2 -M composite, the larger peak area of Pt 2+ (73.9%, as shown in Table S1) suggests that Pt 2+ is the predominant form, likely due to the oxidation by KMnO 4 during the preparation of the material.For Mn 2p, three valence states were observed: Mn 2+ 2p 3/2 and Mn 2+ 2p 1/2 at 640.8 eV and 652.05 eV, Mn 3+ 2p 3/2 and Mn 3+ 2p 1/2 at 641.8 eV and 653.05 eV, and Mn 4+ 2p 3/2 and Mn 4+ 2p 1/2 at 642.8 eV and 654.05 eV [36].The largest peak area corresponding to Mn 4+ (37.6%, as Table S1 shown) suggests that the Mn elements primarily exist in the form of MnO 2 , with a portion of the KMnO 4 precursors being reduced to the lower valence states of Mn 3+ and Mn 2+ [38].The presence of the lower oxidation Mn states (Mn 3+ and Mn 2+ ), as described by Wei et al., may result in the creation of cationic vacancies, which can serve as anchor points for nanoparticles [39].
Molecules 2024, 29,3753 The STEM images in Figure S3a demonstrate a mosaic combination of Au10Pt1 H and MnO2 nanosheets.The element mapping in Figure S3b-e clearly indicates the ence of Au, Pt, Mn, and O elements in the Au10Pt1@MnO2-M composite.The simila tribution of Mn and O elements indicates the formation of a compound (MnO2) t evenly distributed on the surface of Au10Pt1 HSNRs, resulting in the creation Au10Pt1@MnO2-M composite material.The EDS analysis in Figure S3f confirms the ence of elements such as Au, Pt, Mn, and O in the Au10Pt1@MnO2-M composites.
XPS analysis was conducted on the Au10Pt1@MnO2-M composite material to in gate the chemical valence states of each element, as shown in Figure 2. The XPS sp revealed characteristic peaks of Au, Pt, and Mn elements in the samples.There are of O 1s, C 1s, and Na Auger in the XPS pattern (Figure 2a), in which Na may be de from the residual ions after the reaction of sodium citrate and then adsorbed on the nanosheets.Peaks at binding energies of 83.8 eV and 87.45 eV, corresponding to Au and Au 0 4f5/2, respectively [36], indicate the presence of Au in a zero valence state.larly, peaks at 72.05 eV and 75.45 eV are attributed to Pt 0 4f7/2 and Pt 0 4f5/2, while pe 73.45 eV and 76.8 eV correspond to Pt 2+ 4f7/2 and Pt 2+ 4f5/2, respectively [37].In the pre work [35], the Pt element in the structure of Au10Pt1 HSNRs is mainly in a zero-va state, while in the Au10Pt1@MnO2-M composite, the larger peak area of Pt 2+ (73.9 shown in Table S1) suggests that Pt 2+ is the predominant form, likely due to the oxid by KMnO4 during the preparation of the material.For Mn 2p, three valence states observed: Mn 2+ 2p3/2 and Mn 2+ 2p1/2 at 640.8 eV and 652.05 eV, Mn 3+ 2p3/2 and Mn 3+ 2 641.8 eV and 653.05 eV, and Mn 4+ 2p3/2 and Mn 4+ 2p1/2 at 642.8 eV and 654.05 eV [36 largest peak area corresponding to Mn 4+ (37.6%, as Table S1 shown) suggests that th elements primarily exist in the form of MnO2, with a portion of the KMnO4 precu being reduced to the lower valence states of Mn 3+ and Mn 2+ [38].The presence of the oxidation Mn states (Mn 3+ and Mn 2+ ), as described by Wei et al., may result in the cr of cationic vacancies, which can serve as anchor points for nanoparticles [39].The TEM image analysis in Figure 3a illustrates the impact of KMnO 4 additions on the formation of MnO 2 nanosheets.When the addition of KMnO 4 is reduced, only a small quantity of MnO 2 nanosheets are observed.In this scenario, the surface of Au 10 Pt 1 HSNRs interacts with the positively charged cations (e.g., potassium ions) and negatively charged anions (e.g., citrate ions) through electrostatic attraction.This interaction facilitates the formation of connections, resulting in the development of partially longer chain-like structures.Upon increasing the addition of KMnO 4 , a more significant reaction occurs with Na 3 C 6 H 5 O 7 , resulting in the generation of MnO 2 nanosheets that cover the surface of the Au 10 Pt 1 HSNRs, forming an Au 10 Pt 1 @MnO 2 composite structure, as depicted in Figure 3b.With an increased addition of KMnO 4 , a substantial quantity of MnO 2 nanosheets is generated, which subsequently nearly envelop the Au 10 Pt 1 HSNRs, as depicted in Figure 3c.This extensive wrapping of MnO 2 nanosheets around the Au 10 Pt 1 HSNRs could potentially result in the complete coverage of the active sites of noble metals.Such complete coverage is not favorable for catalytic reactions, as it may hinder the accessibility of reactants to the active sites, thereby impacting the catalytic efficiency of the Au 10 Pt 1 @MnO 2 composite structure.
The TEM image analysis in Figure 3a illustrates the impact of KMnO4 additions on the formation of MnO2 nanosheets.When the addition of KMnO4 is reduced, only a small quantity of MnO2 nanosheets are observed.In this scenario, the surface of Au10Pt1 HSNRs interacts with the positively charged cations (e.g., potassium ions) and negatively charged anions (e.g., citrate ions) through electrostatic attraction.This interaction facilitates the formation of connections, resulting in the development of partially longer chain-like structures.Upon increasing the addition of KMnO4, a more significant reaction occurs with Na3C6H5O7, resulting in the generation of MnO2 nanosheets that cover the surface of the Au10Pt1 HSNRs, forming an Au10Pt1@MnO2 composite structure, as depicted in Figure 3b.With an increased addition of KMnO4, a substantial quantity of MnO2 nanosheets is generated, which subsequently nearly envelop the Au10Pt1 HSNRs, as depicted in Figure 3c.This extensive wrapping of MnO2 nanosheets around the Au10Pt1 HSNRs could potentially result in the complete coverage of the active sites of noble metals.Such complete coverage is not favorable for catalytic reactions, as it may hinder the accessibility of reactants to the active sites, thereby impacting the catalytic efficiency of the Au10Pt1@MnO2 composite structure.XPS analysis was conducted on the Au10Pt1@MnO2-H composite sample with the increased addition KMnO4, as depicted in Figure S4.In Figure S4b, the presence of Au in the zero-valent state is observed.The appearance of O 1s, C 1s, and Na Auger is consistent with that in Figure 2a.At this point, Pt in the sample is found to exist in three valence states: Pt 0 , Pt 2+ , and Pt 4+ , as shown in Figure S4c.Notably, Pt 4+ exhibits the largest area (46.7%, as shown in Table S2) in Figure S4c, indicating a higher prevalence of tetravalent Pt.This suggests that with an increase in the amount of KMnO4 addition, Pt elements tend to undergo further oxidation to higher valence states.Mn exists in three valence states: Mn 2+ , Mn 3+ , and Mn 4+ , as illustrated in Figure S4d.In the Au10Pt1@MnO2-H composite material, the excess MnO2 content can cover some of the active sites of Pt, which may result in a decrease in catalytic performance.
After optimizing the addition of KMnO4, the effect of different reaction temperatures on the morphology of the composite material was investigated.In the TEM image presented in Figure 4a, it is evident that at a low reaction temperature of 35 °C, MnO2 nanosheets are not formed.However, the increases in the length of the nanorod structures, possibly due to the electrostatic attraction between the positively charged cations (e.g., potassium ions) and the negatively charged anions (e.g., citrate ions) on the surface of Au10Pt1 HSNRs, led to the formation of secondary connections.Upon increasing the temperature to 45 °C, well-defined MnO2 nanosheets are generated, as shown in Figure 4b.Further elevation of the reaction temperature to 60 °C accelerates the reaction rate, XPS analysis was conducted on the Au 10 Pt 1 @MnO 2 -H composite sample with the increased addition KMnO 4 , as depicted in Figure S4.In Figure S4b, the presence of Au in the zero-valent state is observed.The appearance of O 1s, C 1s, and Na Auger is consistent with that in Figure 2a.At this point, Pt in the sample is found to exist in three valence states: Pt 0 , Pt 2+ , and Pt 4+ , as shown in Figure S4c.Notably, Pt 4+ exhibits the largest area (46.7%, as shown in Table S2) in Figure S4c, indicating a higher prevalence of tetravalent Pt.This suggests that with an increase in the amount of KMnO 4 addition, Pt elements tend to undergo further oxidation to higher valence states.Mn exists in three valence states: Mn 2+ , Mn 3+ , and Mn 4+ , as illustrated in Figure S4d.In the Au 10 Pt 1 @MnO 2 -H composite material, the excess MnO 2 content can cover some of the active sites of Pt, which may result in a decrease in catalytic performance.
After optimizing the addition of KMnO 4 , the effect of different reaction temperatures on the morphology of the composite material was investigated.In the TEM image presented in Figure 4a, it is evident that at a low reaction temperature of 35 • C, MnO 2 nanosheets are not formed.However, the increases in the length of the nanorod structures, possibly due to the electrostatic attraction between the positively charged cations (e.g., potassium ions) and the negatively charged anions (e.g., citrate ions) on the surface of Au 10 Pt 1 HSNRs, led to the formation of secondary connections.Upon increasing the temperature to 45 • C, welldefined MnO 2 nanosheets are generated, as shown in Figure 4b.Further elevation of the reaction temperature to 60 • C accelerates the reaction rate, promoting increased interactions between the MnO 2 nanosheets and resulting in the formation of a large interconnected area in the Au 10 Pt 1 @MnO 2 composite structure, as shown in Figure 4c.At this elevated temperature, the oxidation of Pt elements to higher valence states is enhanced, which could potentially have a detrimental effect on the catalytic performance of the material.
promoting increased interactions between the MnO2 nanosheets and resulting in the formation of a large interconnected area in the Au10Pt1@MnO2 composite structure, as shown in Figure 4c.At this elevated temperature, the oxidation of Pt elements to higher valence states is enhanced, which could potentially have a detrimental effect on the catalytic performance of the material.Based on the experimental findings and analysis, the proposed formation mechanism of the Au10Pt1@MnO2 composite structure is illustrated in Figure S5.In a one-dimensional sol of Au10Pt1 HSNRs containing Na3C6H5O7, the addition of KMnO4 solution triggers a reaction at 45 °C, as follows: Here, C6H5O7 3− is oxidized to CO2 and H2O, while MnO4 − is reduced to form MnO2 nanosheets.The citrate ion protectants present on the surface of Au10Pt1 HSNRs facilitate the growth of MnO2 nanosheets on their surface.As the MnO2 nanosheets continue to grow, the distance between the dispersed Au10Pt1 HSNRs gradually diminishes, ultimately resulting in the formation of an Au10Pt1@MnO2 two-dimensional composite structure by connecting individual Au10Pt1 HSNRs through MnO2 nanosheets.

Electrocatalytic Hydrogen Evolution Performance
The Au10Pt1@MnO2 composite structure was evaluated for its performance in methanol electrooxidation.As shown in Figure 5a, the cyclic voltammetry (CV) curves of different electrocatalysts in a mixed electrolyte of 1 KOH 1 M CH3OH at a scan rate of 10 mV/s were compared.The Au10Pt1@MnO2-M composite structure showed the best catalytic activity, achieving an onset potential of 0.31 V vs RHE and a peak current density of 21.95 mA/cm 2 .In Figure 5b, CV curves normalized by the mass of Pt and Pd elements indicated that the Au10Pt1@MnO2-M composite structure exhibits the best mass activity.The forward scan peak mass activity of the Au10Pt1@MnO2-M composite structure in Figure 5c was 15.52 A mg(Pt) −1 , which was 35.3, 57.5, and 21.9 times higher than that of Pt/C (0.44 A mg(Pt) −1 ), Pd/C (0.27 A mg(Pd) −1 ), and Au10Pt1 (0.71 A mg(Pt) −1 ), respectively, indicating the highest mass activity for MOR.The chronoamperometry (CA) test on the Au10Pt1@MnO2-M composite structure at the potential of the forward scan peak current demonstrated its durability.As shown in Figure 5d, after 4000 s, the MOR mass activity of the Au10Pt1@MnO2-M composite structure was 1.59 A mg(Pt) −1 , which was 12.6, 79.5, and 8.4 times higher than that of Pt/C (0.13 A mg(Pt) −1 ), Pd/C (0.02 A mg(Pt) −1 ), and Au10Pt1 (0.19 Based on the experimental findings and analysis, the proposed formation mechanism of the Au 10 Pt 1 @MnO 2 composite structure is illustrated in Figure S5.In a one-dimensional sol of Au 10 Pt 1 HSNRs containing Na 3 C 6 H 5 O 7 , the addition of KMnO 4 solution triggers a reaction at 45 • C, as follows: Here, C 6 H 5 O 7 3− is oxidized to CO 2 and H 2 O, while MnO 4 − is reduced to form MnO 2 nanosheets.The citrate ion protectants present on the surface of Au 10 Pt 1 HSNRs facilitate the growth of MnO 2 nanosheets on their surface.As the MnO 2 nanosheets continue to grow, the distance between the dispersed Au 10 Pt 1 HSNRs gradually diminishes, ultimately resulting in the formation of an Au 10 Pt 1 @MnO 2 two-dimensional composite structure by connecting individual Au 10 Pt 1 HSNRs through MnO 2 nanosheets.

Electrocatalytic Hydrogen Evolution Performance
The Au 10 Pt 1 @MnO 2 composite structure was evaluated for its performance in methanol electrooxidation.As shown in Figure 5a, the cyclic voltammetry (CV) curves of different electrocatalysts in a mixed electrolyte of 1 M KOH and 1 M CH 3 OH at a scan rate of 10 mV/s were compared.The Au 10 Pt 1 @MnO 2 -M composite structure showed the best catalytic activity, achieving an onset potential of 0.31 V vs RHE and a peak current density of 21.95 mA/cm 2 .In Figure 5b, CV curves normalized by the mass of Pt and Pd elements indicated that the Au 10 Pt 1 @MnO 2 -M composite structure exhibits the best mass activity.The forward scan peak mass activity of the Au 10 Pt 1 @MnO 2 -M composite structure in Figure 5c was 15.52 A mg (Pt) −1 , which was 35.3, 57.5, and 21.9 times higher than that of Pt/C (0.44 A mg (Pt) −1 ), Pd/C (0.27 A mg (Pd) −1 ), and Au 10 Pt 1 (0.71A mg (Pt) −1 ), respectively, indicating the highest mass activity for MOR.The chronoamperometry (CA) test on the Au 10 Pt 1 @MnO 2 -M composite structure at the potential of the forward scan peak current demonstrated its durability.As shown in Figure 5d, after 4000 s, the MOR mass activity of the Au 10 Pt 1 @MnO 2 -M composite structure was 1.59 A mg (Pt) −1 , which was 12.6, 79.5, and 8.4 times higher than that of Pt/C (0.13 A mg (Pt) −1 ), Pd/C (0.02 A mg (Pt) −1 ), and Au 10 Pt 1 (0.19A mg (Pt) −1 ), respectively.This indicates the excellent stability of the Au 10 Pt 1 @MnO 2 -M composite structure for methanol electrooxidation.
A mg(Pt) −1 ), respectively.This indicates the excellent stability of the Au10Pt1@MnO2-M composite structure for methanol electrooxidation.The study evaluated the ability of the catalyst to resist CO poisoning in the electrocatalytic MOR by analyzing the ratio of If/Ib as forward and reverse current densities [40].In Figure S6, the histogram of the If/Ib ratio of each catalyst is presented.The If/Ib ratio of Au10Pt1@MnO2-M was found to be 7.23, which is notably higher than that of commercial Pt/C (5.44), commercial Pd/C (1.93), and Au10Pt1 (4.71).This result indicates that Au10Pt1@MnO2-M exhibits better anti-CO poisoning performance compared to the other catalysts, thereby contributing to improved stability in the MOR reaction.
The study investigated the morphology and structure of composite materials with varying ratios of Au10Pt1 and MnO2 to determine the optimal combination for enhanced electrocatalytic MOR performance.The samples denoted as Au10Pt1@MnO2-L, Au10Pt1@MnO2-M, and Au10Pt1@MnO2-H contained varying amounts of MnO2 nanosheets.As illustrated in Figure S7a, the electrode area-normalized CV curve indicated that the specific activity of the Au10Pt1-MnO2 composite initially increased with the MnO2 content and then decreased with the MnO2 content, the Au10Pt1@MnO2-M showing the highest performance.Figure S7b presents the Pt element quality normalization results, revealing that the peak mass activity of the Au10Pt1@MnO2-M composite was 15.52 A mg(Pt) −1 , which was 1.43 and 2.06 times higher than that of Au10Pt1@MnO2-L (10.83A mg(Pt) −1 ) and The study evaluated the ability of the catalyst to resist CO poisoning in the electrocatalytic MOR by analyzing the ratio of I f /I b as forward and reverse current densities [40].In Figure S6, the histogram of the I f /I b ratio of each catalyst is presented.The I f /I b ratio of Au 10 Pt 1 @MnO 2 -M was found to be 7.23, which is notably higher than that of commercial Pt/C (5.44), commercial Pd/C (1.93), and Au 10 Pt 1 (4.71).This result indicates that Au 10 Pt 1 @MnO 2 -M exhibits better anti-CO poisoning performance compared to the other catalysts, thereby contributing to improved stability in the MOR reaction.
The study investigated the morphology and structure of composite materials with varying ratios of Au 10 Pt 1 and MnO 2 to determine the optimal combination for enhanced electrocatalytic MOR performance.The samples denoted as Au 10 Pt 1 @MnO 2 -L, Au 10 Pt 1 @MnO 2 -M, and Au 10 Pt 1 @MnO 2 -H contained varying amounts of MnO 2 nanosheets.As illustrated in Figure S7a, the electrode area-normalized CV curve indicated that the specific activity of the Au 10 Pt 1 -MnO 2 composite initially increased with the MnO 2 content and then decreased with the MnO 2 content, the Au 10 Pt 1 @MnO 2 -M showing the highest performance.Figure S7b presents the Pt element quality normalization results, revealing that the peak mass activity of the Au 10 Pt 1 @MnO 2 -M composite was 15.52 A mg (Pt) −1 , which was 1.43 and 2.06 times higher than that of Au 10 Pt 1 @MnO 2 -L (10.83A mg (Pt) −1 ) and Au 10 Pt 1 @MnO 2 -H (7.55A mg (Pt) −1 ), respectively.The introduction of MnO 2 nanosheets influenced the electronic structure of the composite structure and enhanced its oxidation ability.The study highlighted the synergistic effect of the composite material, leading to improved electrocatalytic methanol oxidation performance.Additionally, the strong interaction be-tween one-dimensional Au 10 Pt 1 HSNRs and MnO 2 contributed to enhancing the MOR properties [36].In the case of Au 10 Pt 1 @MnO 2 -L, the limited number of MnO 2 nanosheets resulted in a minimal effect on the methanol oxidation process, demonstrating insufficient enhancement of catalytic activity.Conversely, Au 10 Pt 1 @MnO 2 -H contained excessive numbers of MnO 2 nanosheets, which could hinder the performance of the composite by covering active Pt sites and affecting the composition and electronic structure.Ultimately, Au 10 Pt 1 @MnO 2 -M demonstrated the optimal ratio of Au 10 Pt 1 to MnO 2 , exhibiting the best electrocatalytic methanol oxidation performance among the samples studied.
Figure S8 presents a histogram illustrating the I f /I b ratio of the catalyst for MOR.The I f /I b ratio of the Au 10 Pt 1 @MnO 2 -L sample was the highest at 9.52, indicating a strong ability to resist CO poisoning.However, this sample exhibited lower activity.The I f /I b ratio of Au 10 Pt 1 @MnO 2 -M was higher than that of Au 10 Pt 1 @MnO 2 -H, indicating that it possessed better resistance to CO poisoning compared to that of the latter sample.Therefore, when the ratio of Au 10 Pt 1 to MnO 2 nanosheets is moderate, the overall performance is better.This finding underscores the importance of balancing CO poisoning resistance and activity in catalyst design.The Au 10 Pt 1 @MnO 2 -M sample, with its moderate ratio of components, demonstrated improved comprehensive performance in terms of CO poisoning resistance and activity for the MOR.

Materials
All the reagents were used directly as received from the suppliers, without further treatment.Hydrogen tetrachloroaurate tetrahydrate (HAuCl

Synthesis of Au NPs
The synthesis of Au NPs was carried out through a citrate reduction process [41].In a typical procedure, 1 mL Na 3 C 6 H 5 O 7 solution (0.01 M/L) and 415 µL of HAuCl 4 solution (0.024 M) were added to 37 mL of ultrapure water and vigorously stirred.Subsequently, 1 mL of ice-bathed NaBH 4 solution (0.1 M) was added after 5 min, resulting in a color change in the solution from pale yellow to ruby red upon completion of the reaction.The solution was then left undisturbed for 2 h to age, yielding Au NPs sol (0.05 mg/mL) with a particle size of 6-8 nm.

Synthesis of Au 10 Pt 1 HSNRs
In a quartz photoreactor, 40 mL of Au NPs sol was introduced into 10 mL of ultrapure water and stirred vigorously to achieve a homogeneous mixture.Subsequently, 50 µL of NaOH (0.1 M) and 53 µL of H 2 PtCl 6 (0.019 M) were added to the solution.The mixture was then subjected to visible light irradiation (≥400 nm) for 0.5 h in a water bath at 15 • C. Subsequently, the solution was allowed to react at 45 • C in the dark for 24 h, without agitation, to yield Au 10 Pt 1 HSNRs.The experimental setup employed an Xe lamp (PLS-SXE300 +/UV), sourced from Beijing Perfect Light Technology Co., Ltd.(Beijing, China).

Synthesis of Au 10 Pt 1 @MnO 2 Composites
The synthesis procedure for the Au 10 Pt 1 @MnO 2 composite involves several steps.Initially, 50 mL Au 10 Pt 1 HSNRs is stirred in a beaker.Subsequently, 0.5 mL of KMnO 4 (0.014 M) solution is introduced.The mixture is stirred and homogenized in a 45 • C water bath for 2 h.Upon completion of this process, the resulting composite mate-rial is designated as Au 10 Pt 1 @MnO 2 -M.Additional samples incorporating varying amounts of KMnO 4 , specifically 0.25 mL and 1 mL, are labeled as Au 10 Pt 1 @MnO 2 -L and Au 10 Pt 1 @MnO 2 -H, respectively.

Materials Characterization
The X-ray photoelectron spectra (XPS) were acquired using the K-Alpha+ XPS system on a thermo ESCALAB250Xi instrument (Axis Ultra DLD Kratos AXIS SUPRA; PHI5000versaprobeIII) outfitted with an X-ray source of Al Kα radiation and calibrated with respect to C 1s at a binding energy (BE) of 284.6 eV from contaminant carbon.The XPS sample was prepared using the drop-casting method, and the sol sample was directly cast on a 5 × 5 cm 2 monocrystalline silicon sheet with a dropper.The structure and morphologies of the samples were examined using field emission high resolution transmission electron microscopy (FE-HRTEM, JEM-2010F and Tecnai G2 F20).For the preparation of the TEM test samples, a drop-casting method was employed, and the sol was directly deposited onto a standard carbon support film using an eyedropper.After allowing the sample to dry, it was subsequently placed in the sample holder for analysis.Energy dispersive X-ray (EDX) analysis and elemental mapping were performed using the X-max T80 system from Oxford instruments.The ultraviolet−visible (UV−VIS, diffuse reflection absorption spectra) data were recorded in the spectral region of 200-1400 nm using a unico UV-2600 spectrophotometer (Shimadzu, Japan).All the UV−VIS samples in this work are sols, which can be tested directly in quartz colorimetric dishes.

Evaluation of Electrocatalytic Activity
The fabrication process of the working electrode involved the following steps: Initially, 0.02 g of conductive carbon black (Vulcan XC-72, Cabot) was combined with the Au 10 Pt 1 @MnO 2 solutions and subjected to ultrasonic agitation for adsorption over 24 h.The mixture was then filtered and dried.Subsequently, 1 mg of the catalyst obtained in the previous step (or commercial Pt/C, Pd/C catalyst) was added to a spiral glass bottle containing 0.48 mL water, 0.5 mL ethanol and 20 µL Nafion solution (5.0 wt.%), and ultrasonically stirred for 2 h to obtain the uniformly dispersed catalyst slurry ink.Finally, the 5 µL catalyst paste was dropped five times onto a 3 mm diameter, polished, and cleaned L-shaped glass carbon electrode.After natural drying, a uniform catalyst film was formed on the electrode surface.
The evaluation of the electrochemical methanol oxidation reaction (MOR) was conducted at a controlled temperature of 25 • C using a single-chamber electrolytic cell equipped with a three-electrode system and a CHI660E electrochemical workstation from Shanghai CH Instrument Co., Ltd., Shanghai, China.A platinum sheet electrode and a saturated calomel electrode (SCE) were selected as the counter electrode and the reference electrode, respectively.The electrochemical tests for the MOR were performed in 1 M KOH and 1 M CH 3 OH electrolytes saturated with N 2 .Prior to the electrochemical test, the activated working electrode underwent 20 cycles of voltammetric scanning at a rate of 50 mV/s.The performance assessment was carried out at a scanning rate of 5 mV/s, and the cyclic voltammetry curve was recorded.The stable test voltage corresponded to the overpotential at the maximum current density.All potentials mentioned in this study are referenced to the SCE reference electrode.Commercial Pt/C and Pd/C (JM, 20%) were utilized as the reference catalysts.

Conclusions
In summary, the study focused on synthesizing Au 10 Pt 1 @MnO 2 composites using a wet chemical method, successfully maintaining the one-dimensional structure of Au 10 Pt 1 HSNRs while incorporating lamellar MnO 2 .The quantity of the KMnO 4 added and the reaction temperature were crucial factors in the formation of MnO 2 .The inclusion of MnO 2 nanosheets significantly influenced the electronic structure of the composite, with MnO 2 contributing to the oxidation capacity and enhancing the overall material properties,

Figure 5 .
Figure 5.The performance of different catalysts for MOR in 1 M KOH and 1 M CH3OH solutions: (a) CV curve of specific activity; (b) CV curve per mass of noble metals; (c) mass activity at the highest current density; (d) chronoamperometry measurement curves.

Figure 5 .
Figure 5.The performance of different catalysts for MOR in 1 M KOH and 1 M CH 3 OH solutions: (a) CV curve of specific activity; (b) CV curve per mass of noble metals; (c) mass activity at the highest current density; (d) chronoamperometry measurement curves.